This proposal is a supplement to NIH Grant #1 RO1 CA25323-01, which was awarded for three years beginning April 1, 1979. The existing grant was funded primarily to provide a clinical evaluation of ultrasonic computed tomography of attenuation and velocity in the breast as a method of diagnosing cancer. Those clinical trials are now under way and progressing well with system improvements promised in the proposal for that grant. The primary purpose of this supplemental proposal is to develop and evaluate attenuation images that provide an accurate measure of the attenuation coefficient as a bulk property of the tissue. While the present edge enhanced images increase detectability of lesions in some cases and contribute to the diagnosis in combination with the velocity images, it is very important that a more quantitatively and spatially accurate attenuation image be developed and included in the clinical trials. The new attenuation images will be obtained with a phase independent array and a simple, new signal processing. The new imaging technique will be operating reliably for full clinical trials no later than 18 months after the initiation of the supplemental effort. In the remaining 15 months of the supplement, at least 75 patients with a high probability of breast cancer will be imaged with new and existing UCT techniques for comparison with pulse echo images, mammography and histologic findings. The phase insensitive array technique and other new methods proposed by this group and others for attenuation and velocity UCT imaging will be compared. These various signal processing techniques will be implemented digitally for evaluation on the same few sets of data from realistic test objects and breast tissue samples. In addition, methods proposed for reconstruction of velocity images from backscatter data will be evaluated using the same test object.